There is a continuing demand for low cost procedures for the coloration of molded plastics, especially reinforced polyester articles in such industries as the automotive, home appliance, radio and television industries and for use in decorative containers and the like. The recent development of moldable reinforced polyester compositions characterized by little or no tendency to shrink during the curing thereof has brought with it the demand for suitable methods for the coloration of molded articles. Such polyester compositions are usually heterogeneous in nature, that is they are formulated to contain not only reinforcing materials, i.e., fiber glass and inorganic diluents such as talc, asbestos and the like, but also two or more dissimilar organic polymer materials, e.g., mixtures of unsaturated polyesters with saturated polyesters, polymethyl methacrylate, polyvinyl chloride, polystyrene or the like. On curing of the unsaturated polyester component as by cross linking with styrene or other ethylenic monomers, the dissimilar polymeric materials separate as a distinct phase giving rise to a distinctly heterogeneous polymer composition. Although on molding such polymer compositions, articles of superior surface smoothness and low shrinkage can be obtained, the heterogeneous nature of the composition creates problems in the coloration of such articles.
Thus, on attempting to color the polymer composition by conventional pigmenting procedures results in uneven coloration of the molded article due most likely to differences in the solubility or dispensibility of the pigment in the dissimilar polymers. Dyeing of these articles by conventional procedures also results in uneven colorations due to the dissimilar attraction of the polymers for the dyestuff or the dyeing procedure may result in damage to the smooth surface of the molded article.